Saturday, November 24, 2018

Metallic iron and the origin of metabolism

Over the years I've been convinced that carbon monoxide derived formaldehyde/formate are probably the initial molecular precursors of acetate at the origin of life. All that is needed is a supply of electrons at a sufficiently negative potential to reduce CO2 to CO and so to CH2O then to HCOOH, formate. Clearly a 1.5 volt battery applied across an anoxic CO2 rich reactor might do this. In the Life series of posts the best candidate in reality is the alkaline hydrothermal vent environment such as the Lost City complex, working under anoxic, CO2 rich Hadean ocean conditions.

This paper:

Native iron reduces CO2 to intermediates and endproducts of the acetyl-CoA pathway

from a french institute, suggests that metallic iron alone might provide electrons of sufficiently negative potential to perform the process, this is the basic premise:

Fe0  Fe2++ 2e-

These electrons have a sufficiently negative potential to allow:

CO2 + 2e+ H2 HCOOH + O2-

Obviously the Fe2+ would combine with the O2- to give FeO, leaving a formate moiety as the start of the process essential for the origin of pre-biotic metabolism.

In the event the two most common experimental products were acetate and pyruvate, a highly plausible step or two onward from formate, which they also found under certain conditions.

The circumstances of temperature and pressure were, in some experiments, plausible for pre-biotic chemistry.

The problems, compared to the Lane and Martin hydrothermal vents concept, seem to be:

The products are bound to the surface of the iron deposit, potassium hydroxide was needed to hydrolyse them off for measurement.

The process is reactive rather than catalytic, ie the metallic iron is consumed in the process of providing electrons. This contrasts starkly with the continuous supply of electrons supplied by hydrothermal vent conditions over geological time scales.

Then there is the concentration problem. If the organic products were to be freed from the iron surface they need to be somewhere other than the open deep ocean or they will simply be lost by dilution.

Finally the group did not cite any of the work from Nick Lane and his lab excepting one rather general review link. Naughty.

So. Some interesting chemistry and it's good to have multiple groups thinking about a given problem but I don't see the hydrothermal vent hypothesis being abandoned any time soon. Certainly not by believers like myself.


No comments: